Intersection traffic controller



5 Sheets-Sheet l Filed April 16, 1964 DAN/EL 65mm/6H JAMES .5. @apoE/vBY Y A v70/ems V5 July 25, 1967 D. L.. GERLOUGH ETAL 3,333,240

INTERSECTION TRAFFIC CONTROLLER 3 Sheets-Sheet 2 Filed April 16, 1964 1w. l: wwi i: SMN ZMS? lh. RU M y h uw 1imom E QZ i Nm@ 7M ww E www m'lvl oa vw. H B A L5 zozu, AO :E w O@. llkfmj w Mm s 5% B v f w MS l N@-NI N |.NN o@ Emmkw r 1 l @2Q/H@ lvllll 1| EN SNN @da :i: 023cm mm3 .NN..523 J ZWAOWC|ZOU DZO IFQOZ Q NF d3ou 20mn, wm .pu @n A wmmww a a 4 a 1J m .W1 bm W W @umm M M @M wwwwwwwww m a a 1 ozsomjom mv m-\ @m Nv n m ZA ozsom S 3 Sheets-Sheet 5 July 25, 1967 D. l.. GERLOUGH ETALINTERSECTION TRAFFIC CONTROLLER Filed April I 16, 1964 A WOR/vf vsUnited States Patent O 3,333,240 INTERSECTION TRAFFIC CONTROLLER DanielL. Gerlough, Pacific Palisades, and James B. Rudden, Canoga Park,Calif., assignors to The Bunker- Ramo Corporation, Canoga Park, Calif.,a corporation of Maryland Filed Apr. 16, 1964, Ser. No. 360,270 14Claims. (Cl. 340-36) This invention relates to a signal system forcontrolling tratlc ow at an intersection, and more particularly, to asystem for automatically controlling traic flow through an intersectionin accordance with the demands of traffic volume.

Achieving eilicient traic ilow at an intersection is difcult sincevehicular flow moving in one direction through the intersection.intereferes with that moving in other directions. Without effectivecontrol, the vehicles using the intersection may Ibe subjected tounnecessary delays and hazards.

Traffic control at an intersection may be provided by stop signs, simpletraftlc signals with a xed cycle, or very complex signal systemsresponsive to the volume of traiiic How in the diierent directions. Theetliciency of any such control system may be measured by considering theaverage delay of all vehicles passing through the intersection.Accordingly, a system is improved if made responsive to the volume oftraic approaching from each direction so that fewer vehicles aredelayed. For this purpose, present automatic control systems frequentlymake use of predictive information based upon analyses of the dailytratiic ow at the intersection. Unfortunately, the traic actuallypresent at a certain time or any given day may frequently varyconsiderably from that predicted.

In particular, traiiic responsive control systems are commonly used tocontrol four-way trac at major intersections along a primary street, theintersecting street being termed a secondary street. The control systemprimarily operates periodically to interrupt the flow of traffic alongthe primary street to permit those vehicles approaching on the secondarystreet to pass through the intersection.

In addition, some of the vehicles approaching the intersection on theprimary street may want to turn across the oncoming trac onto thesecondary street. In places such as the United States, where vehiclesdrive to the righthand side of the road, this would vbe a left turnmaneuver. Systems operating to permit such left turns may actually speedtraffic ilow through the intersection under some light traflicconditions. Left turns should, however, be prohibited in most instancesby the control system Whenever the oncoming trac ow is heavy. Becauseboth oncoming and secondary street traffic must be stopped for leftturns, the system efliciency is substantially decreased should leftturns be permitted during periods of heavy traflic flow.

Therefore, it is an object of the present invention to provide animproved traflc control system for regulating vehicular flow atintersections.

Another object of the present invention is to provide an intersectiontratlic control system responsive to the actual dow of trac in thedifferent directions.

A further object of the invention is to provide an improved trac controlsystem for intersections which is responsive to the delay of approachingtrac.

Yet another object of the present invention is to provide an improvedtratic control system, which is responsive to the flow of traiiic foretiiciently controlling left turn maneuvers.

These and other objects are accomplished in accordance with theinvention by comparing the time average of the number of vehiclesapproaching the intersection in a given direction with given standardsto determine the ICC most efficient manner of operating the intersectioncontrol system. The intersection control system then automaticallyresponds to the results of the comparisons to eliiciently control the owof vehicular trailic.

In accordance with particular aspects of the invention as shown by theembodiment described herein, the trafc control system in accordance withthe invention efiiciently controls vehicles approaching the intersectionfrom one direction on the primary street and desiring to turn lefit ontothe secondary street. A time average of the number of Vehiclesapproaching the intersection from the oncoming direction is firstcompared with a preset standard to establish whether left turns shouldbe allowed or not. If the time average exceeds the preset standard, leftturns are forbidden under all conditions; if the time average does notexceed the preset standard, left turns are allowed conditionally.

The time average of the number of vehicles approaching the intersectionfrom the oncoming direction is also compared with a time average of thenumber of vehicles waiting to make a left turn. Whenever the timeaverage of the number of left turning vehicles exceeds that of theoncoming vehicles during a time at which left turns are permittedconditionally, the signal system operates to stop both the oncomingtraiic and traiiic on the secondary street to permit the left turn.

A better understanding of the present invention may be had by referenceto the following detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a simplied block diagram illustration of an intersectiontratiic control system in accordance with the invention;

FIG. 2 is a detailed circuit diagram illustrating vehicle detectioncircuits, comparison circuitry, and a relay-operated left turn controlsignal in accordance with one particular embodiment of the invention;and,

FIG. 3 is a detailed circuit diagram of a four-way trafc control signal,which is interconnected with the circuitry of FIG. 2 to form aparticular embodiment of an intersection tratiic control system inaccordance with the invention.

It should be understood that the general principles described herein areapplicable to various intersecting trafic situations. For example, theprimary and secondary directions need not actually be differentdirections, but may be deemed to apply to any two interfering trafc ows.Thus, if two parallel lanes of traflc, both traveling in the samedirection, converge or interefere, the point at Which they merge isdeemed an intersection within the meaning of this general description.

Referring now to FIG. l, which illustrates in simplified block diagramform the function or units of a trafic control system 'm accordance withthe invention, the iiow of vehicles through an intersection from aprimary direction and from a secondary direction is regulated by thetraic control signal circuit 10. Stop, go and caution light displays aremounted at appropriate locations in the vicinity yof the intersection soas to be visible to the vehicles approaching from the diiferentdirections. Each light display is operated selectively by the controlcircuit 10 to permit the trafc -to flow in either the primary or theseconda-ry direction. In certain instances, the control circuit 10 maybe used to control the operation of additional signals 11, such as turnsignals, or may be made responsive to signals from an external controlunit 12, such as either a central computing system for controlling traicin a network of intersecting streets or a local program unit foroperating the particular control unit according to estimated conditions.

A vehicle sensing unit 14 is provided to sense the number of vehiclesapproaching the intersection from the primaryrdirection, while a similarvehicle sensing unit 16 determines the number of vehicles approachingthe intersection from the secondary direction. The approaching vehiclesshould be understood to include not only those moving towards theintersection, but those that are stopped awaiting a change of signal. Inother words, the sensing units 14 and 16 measure the total number ofvehicles in a selected portion of the respective street adjacent theintersection, and provide the outputs NP and NS which are proportionalto the number measured. These outputs NP and NS are applied to theinputs of respective time averaging circuits 18 and 2 0, which produceoutput levels Ep and ES lrepresenting a time average of the number ofvehicles approaching the intersection from the primary and secondarydirections.

A preset output level EL of constant magnitude is obtained from a presetlevel source 22 to be compared with the primary direction time averageoutput EP in a comparator 24. When the level of the time average outputEP is greater than the preset level EL, the signal level comparator 24produces a first comparator output EP EL to actuate a forbiddensecondary signal 26. The forbidden secondary signal 26 is a visualdevice for indicating to motorists approaching the intersection in theseconda-ry direction that they will not be allowed to pass through theintersection under present conditions. For convenience, the signalshould be displayed toV provide a timely warning to the approachingmotorists, thereby permitting them to choose an alternative routeavoiding Vthe intersection. Such a device might, for example, take theform of a No Left Turn sign in some instance or a Do Not Enter sign inothers.

A second comparator output EL E1.1 is obtained from the comparator 24whenever the time average output level EP is smaller than the presentlevel EL. This com pa-rator output EL EP may be coupled to actuate apermissive secondary signal 28 and enable an AND gate circuit 30.

The time average output level EP is also applied to a second signallevel comparator 32 to be compared with the other time average outputlevel Es from the time averaging circuit 20. Whenever the time averageoutput level is greater than Ep, a comparator output ES EP is generatedto be applied to the other input terminal of the AND gate 30. If the ANDgate is enabled by the EL EP comparator output from the comparator 24,then the ES EP 4comparator output is delivered through t-he AND gate 30to the traiiic signal control circuit 10. After a proper delay intervalprovided by the control circuit 10, the ES EP comparator output actuatesa go secondary signal 34 while at the same time operating the varioussignal displays under the control of the control circuit to stop traicflow in the primary direction so as to permit the uninterrupted ow ofvehicles through the intersection in the secondary direction.

Referring now to PIG. 2, a detailed circuit diagram is shownillustrating a particular embodiment of an intersection tratiic controlsystem in accordance with the invention. The intersection, which isshown generally to Y aid in the following description, is of the typeyfrequently found, having a primary and a secondary street intersectingone another at right angles. The primary street has separate lanes forboth northbound and southbound vehicles, which travel in oppositedirections separated by a center divider or a Icenter marker 36,'Thesecondary street likewise carries separate lanes of eastbound andwestbound traic on opposite sides. A righthand drive convention isassumed, and the direction of traic flow is shown by the directionalarrows 38.

Northbound traic approaching the intersection may be separated into aplurality of lanes, of which the far left lane nearest the centerdivider 36 is used by those vehicles desiring to turn left at theintersection. In order to simplify the illustration, southbound trafficis assumed to move in only a'single lane. Also, it is assumed thatsouthbound at other times it is comparatively light. When southbound Ytraffic is light, permitting left turns from the extreme left northboundlane to the secondary street speeds the ow of traflic through theintersection, whereas during periods of heavy southbound traic such leftturns should not be permitted.

A bank of relays 42, operated by vehicle presence kdetectors (notshown), is arranged to provide an output voltage directly proportionalto the number of southbound vehicles approaching the intersection. Eachrelay consists of movable contact 44 for contacting either of two xedcontacts, one upper contact and one lower contact as 4shown in thedrawing of FIG. 2. Each of the upper contacts is connected through alike resistor 45 to a source of positive potential, and thelowercontacts are connected through equal individual resistors 46.to

, ground potential. The vehicle presence detectors are of the well konwnmagnetometer variety or may be of any other conventional construction,and are accordingly not shown in detail herein. The Yvehicle presencedetectors are spaced apart by approximately one vehicle length startingat the iirst vehicle position adjacent the intersection and extendingnorthward along the southbound lane. Each vehicle presence detectoroperates its respective movable contact 44 to engage the lower fixedcontact when no vehicle is present and to engage the upper fixed contactduring the time that a vehicle is present. A center conductor 48connects all of the movable contacts together, so that the voltageappearing on the center conductor 48 is in direct proportion to thenumber of southbound vehicles approaching.

Another bank of relays 50 is -used with another set of vehicle presencedetectors disposed in the far left northbound lane. A number of movablecontacts 52 are each operated -by an associated vehicle presencedetector to move between upper and lower tixed contacts, as shown in thedrawing. The upper fixed contacts are connected through like resistors54 to another source 'of positive potential, and the lower fixedcontacts are connected through equal resistors 56 to ground potential.The vehicle presence detectors (not shown) are disposed in thenorthbound lefthand lane, and are spaced apart by one vehicle lengthbeginning at the rst vehicle position adjacent the intersection. Whenthe presence of a vehicle lis sensed by one of the vehicle presencedetectors, the associated movable contact 52 is moved to the upperVfixed contact to connect a central conductor 58 to the source ofpositive potential through one of the resistors 54. Accordingly, thevoltage appearing on the center conductor 58 is directly proportional tothe number 'of the northbound vehicles approaching the intersection orwaiting in the far Vleft lane.

The two voltage levels on the center conductors 48 and 58 are coupled toa time averaging and comparing circuit 60. The voltage level 'on thecenter conductor 58 is coupled through 4a variable resistor -62 tocharge an integrating capacitor 64. The setting of the variable resistor62 determines the time constant of the time averaging circuit, since thecurrent flow through the resistor 62 is directly proportional both toits resistance value and to the voltage difference between the charge onthe capacitor 64 and the voltage level on the center conductor 58. Thevoltage on the capacitor 64 is coupled to the control grid of a triodeelect-ron tube 66 connected in conventional cathode follower fashion. Y

In similar fashion, the voltage level on the center conductor 48 iscoupled through a variable resistor 68 to charge an integratingcapacitor 70', the time constant of the charging circuit Ibeingdetermined by the setting of the resistor 68. The voltage on thecapacitor 70 is coupled to the control grid of another triode vacuumtube 72, also connected in cathode follower fashion. Y

The outputs from the cathode followers are connected together throughthe actuating coil of a 4relay 74 and .a`

series-connected diode 76. The diode 76 is poled to conduct in theforward direction only when the voltage at the cathode of the tube 66exceeds the voltage at the cathode of the tube 72. When current does Howthrough the diode 76, the relay 74 is actuated to close a normally-openrelay switch 78.

The voltage produced at the cathode of the tube 72 is also coupledthrough another diode 79 and an actuating coil of a relay 80 to becompared with a preset voltage level. This preset voltage level isdetermined by the setting of a movable contact arm on a potentiometer82, which has its end terminals connected between a source of positivepotential and ground. The diode 79 is poled to permit current flow inthe forward direction only when the voltage from the cathode of the tube72 exceeds the preset voltage level, so that then the relay 80 isactuated to swich a movable contact 84 from its normal engagement withan upper contact to engage a lower contact. Thus, the positive voltageapplied to the movable contact 84 is applied to either the upper orlower xed contact, depending upon whether or not the relay 80 isactuated.

The operation of the time averaging and comparing circuit 60 is asfollows: Voltage levels equal to the number of northbound vehicles inthe left lane and to the number of southbound vehicles are applied viathe center conductors 58 and 48 to the circuit 60. The voltage level onthe center conductor 58 is time averaged =by the integrating action ofthe resistor 68 and the capacitor 70 to produce a voltage signal at thecontrol electrode of the tube 72, which voltage signal is an accuratemeasure of the current volume of southbound traffic ow. The voltagelevel produced on the center conductor 58 for northbound traffic is timeaveraged in a similar manner by the variable resistor 62 and itsassociated integrating capacitor 64, so that a voltage signal is appliedto the control electrode of the tube 66, which signal is representative'of the volume of traic ow in the northbound lane intending to turnleft.

The cathode follower circuits including the tubes 72 and 66 exhibit ahigh input impedance and a low output impedance, so that the loadexhibited by the succeeding cornparison and switching circuitry does notaffect the charge on the associated capacitors 64 and 70.

The -voltage produced at the cathode of the tube 72 represents a timeaverage of the southbound ilow of traic, which is compared with thepreset level by means of the diode 79. Thus, whenever the southboundtrailic ow is sufficiently heavy, current ows through the diode 79 toactuate the relay 80, thereby applying a positive signal through thelower xed contact to indicate a no left turn condition. During periodsof light southbound traic flow, however, the positive voltage is appliedto the upper iixed contact through the movable contact 84 to indicate acondition in which left turns are permitted.

The voltage levels at the cathodes of the tubes 72 and 66 are alsocompared to each other through the diode 76. Accordingly, whenever thetime average voltage level representing northbound traffic Waiting toturn left exceeds the time average voltage level produced by thesouthbound traic, the current owing through the diode 76 actuates therelay 74 to close the associated normally open relay contact 78. Theupper fixed contact for the movable relay contact 84 is coupled to thexed contact for the movable relay contact 78. Therefore, if the relay 80has not been actuated by heavy southbound trac, the positive voltage isapplied through the movable contacts 84 and 78 to indicate that a leftturn operation should begin.

A left turn signal unit 86 receives the positive voltage indicationsfrom the time averaging and comparing circuit 60. A positive voltageapplied to the lower xed contact of the movable contact 84 is applieddirectly as a no left turn indication to actuate a no left turn signaldisplay 88. On the other hand, if the movable contact 84 is against theupper xed contact, the no left turn signal display 88 is no longeractuated and the positive voltage is now applied directly to actuate aleft turn on arrow only signal display 90 to indicate that left turnsare permitted. If the relay 74 should then be actuated, the positivesignal would also be applied as a turn left indication to initiate asequence of events for actuating the turn left .arrow signal display 92.A positive turn left indication actuates a -relay 94 to move two movablecontacts 96 and 98 to their lower positions. In the normal upperposition, the movable relay contact 96 is connected to ground potentialthrough the upper fixed contact, whereas the other movable relay contact98 connects its upper fixed contact to ground. When the relay 94 isactuated, the movable contact 98 removes the ground potential from itsupper fixed contact and the movable contact 96 is disconnected fromground .and coupled to receive a positive current flow through a diode102.

The positive turn left indication is also applied through a variableresistor 104 to gradually charge a capacitor 106. Alternatively, thecapacitor 106 may be quickly charged by a current through small resistor108, the movable relay contact 96 and the diode 102.

The voltage on the capacitor 106 is coupled to the control grid of `atriode gating tube 110, which has its cathode connected in series withthe actuating coil of a relay 112. A pair of resistors 114 and 116 forma voltage divider circuit between the ground potential and the positiveplate supply for tube 110, and the cathode of the tube 110 is connectedto the junction between the two resistors. Thus, the tube 110 remainsnon-conductive until the capacitor 106 attains a charge in excess of thecathode voltage, at which time it becomes conductive to actuate relay112. The relay 112 controls the position of two movable relay contacts118 and 120, the movable contact 120 normally applying a groundpotential to its upper contact and the movable Contact 118 normallybeing disconnected from its lower iixed contact. Upon actuation, therelay 112 disconnects the movable contact 120 to remove the groundpotential from its upper xed contact and connects the movable contact118 to the left turn arrow signal display 92 through its lower xedcontact.

The entire operation of the left turn signal unit 86 may best beunderstood by rst referring to the details of the four-way trafficcontrol signal unit 122, as illustrated in FIG. 3. The four-way signalunit 122 contains four separate red, yellow and green signal lightdisplays 124, 125, 126 and 127. These signal displays may be mounted inconventional fashion to provide stop, caution and go visual commands tomotorists approaching the intersection from each of the four directions.As indicated in the drawing, the signal display 124 is for eastbound(E.B.) traic, signal display 125 for westbound (W.B.), signal display126 for northbound (N.B.), and signal display 127 for southbound (S.B.)traic. Each of the lighting displays 124-127 is provided with a separaterelay circuit for supplying a positive illuminating voltage toselectively display one of the three lights. The relay circuits areoperated under the control of a pair of flipop circuits 128 .and 130 anda pair of relay circuits 132 and 134. The details of the four-waytraffic control signal unit may thus be understood by reference to atypical operating sequence.

The ilip-op 128 consists of two triode tubes 136 and 137 connected in aconventional ilip-tlop arrangement, and the tlip-op consists of thetriode tubes 138 and 139 connected in like manner. The actuating coil ofa relay 140 is -coupled in the anode circuit through the tube 137, andthe actuating coil of a relay 141 is connected in the anode circuit ofthe tube 139.

Initially assume that the relays 140 and 141 are not energized, sincethe tubes 137 and 139 of the flip-hops 128 and 130 are not conducting.Two movable contacts 143 and 144, which are operated by the relay 140,and

the movable contacts 146 and 147, which are operated by the relay 141,are all in their normal upper positions engaging the upper fixedcontacts. The movable contact 143 applies a positive voltage to a pairof relays 149 and 151 associated with the eastbound and westboundvsignaldisplays 124 and 125, respectively. The relays 149 and 151 are energizedto connect their associated movable contacts 153 and 155, respectively,to the green signals of the signal displays 124 and 125.

In a similar-fashion, the positive voltage is also applied through themovable contact V147 to energize a pair of relays 157 and 159.Energizing the relay 157 causes a positive voltage to be applied throughan associated movable contact 161 to the movable contact 153 to lightthe green signal of the eastbound display 124. Similarly, the energizedrelay 159 switches an associated movable contact 163 to its lower fixedcontact to apply the positive illuminating voltage through the movablecontact 155 to the green signal light on the westbound display 125.

While in this initial condition, no signal is being applied to energizerelays 165 and 167 associated with the northbound display 126 or torelays 169 and 171 associated with the southboundrdisplay 127.Accordingly, a movable contact 173 operated by the relay 165 remains inits upper position to apply the positive illuminating voltage to the redsignal light of the northbound display 126, while a movable contact 175operated by the relay 169 applies the positive illuminating voltage tothe red signal light of the southbound display 127.

The illuminating voltage applied to the green signal on the westbounddisplay 125 causes a current fiow through a variable resistor 173 and aseries connected diode 174 to begin charging a capacitor 176. At the endof a given timing interval, determined by the setting of the variableresistor 173, the voltage across the capacitor 176 becomes sufiicient tocause a gating tube 178, normally cutotr', to conduct. The actuatingcoil of a relay 180 is coupled in the anode circuit of the tube 178 tobe actuated upon conduction to switch a pair of movable contacts 181 and182. The movable contact 182 is switched to apply a ground potential todischarge a capacitor 176. The movable contact 181 is switched to applya positive pulse through the movable contact 146 to the control grid ofthe tube 137, thereby causing the tube 137 of the fiipflop 128 toconduct and the tube 136 to cutoff. The relay 140 is actuated by thecurrent ow through the tube 137 to switch the movable -contacts 143 and144 to their lower fixed contacts.

Switching of the movable contact 143 causes the relays 149 and 151 to bedeenergized so that the eastbound and westbound green signals areextinguished so that the illuminating voltage is applied to the yellowsignals. At lthe same time, the positive voltage is applied by themovable contact 143 to energize the relays 167 and 171 to connect amovable contact 184 through its lower fixed contact to the green signalof the northbound display 126 and to connect a movable contact 186through its lower fixed contact to the green signal of the southbounddisplay 127.

The illuminating voltage applied to the westbound yellow signal is alsoapplied through a variable resistor When the tube 139 conducts, therelay 141 is energized -to switch the position of the movable contacts146 and 147. The positive voltage on the movable contact 147 is removedfrom the relays 157 and 159, which are then deenergized. When theassociated relays 157 and 159 deenergize, the movable contacts 161 and163 return to their upper fixed contacts to apply the illuminatingvoltage to the eastbound and westbound red signals, while alsoextinguishing the eastbound and westbound yellow signals. The positivevoltage now applied to the lower fixed -contact by the movable contact147 energizes the relays 165 and 169 so that the illuminating voltage isremoved from the northbound and southbound red signals and applied tothe movable contacts 184 and 186, which have been previously switchedinto engagement with their lower fixed contacts, to illuminate thenorthbound and southbound green signals.

The voltage illuminating the southbound green signal is also appliedthrough a variable resistor 198 and a Y Y applied to energize the relays149 and 151, while the 187 and a series connected diode 188 to begincharging a capacitor 190 in the timing circuit 132. After a chosentiming interval determined by the setting of the variable resistor 187,the voltage across the capacitor causes a gating tube 192 to conduct. Arelay 194 connected in the anode circuit of the tube 192 operates a pairof movable contacts 196 and 197. With the relay 194 energized a groundpotential is applied through the movable contact 196 to discharge thecapacitor 190, while a positive pulse is applied by the movable contact197 through the movable contact 194 to the control grid of the tube 139in the fiip-op 130. The positive pulse causes the tube 139 to conductand the tube 138 to cutoff.

relays 167 and 171 are deenergized. The movable contacts 184 and 186move upward to remove the illuminating voltage from the northbound andsouthbound green signals and apply it to the northbound and southboundyellow signals. The movable contacts 153 and 155 nowv contact theirlower fixed contacts to prepare for the next eastbound and westboundgreen indication due to the reenergization of the associated relays 149and 151.

The voltage illuminating the northbound yellow signal is also appliedthrough a variable resistor 201 and a series connected diode 202 toagain charge the capacitor 190. After the interval determined by thesetting of the variable resistor 201, the relay 194 is energized byconkduction of the tube 192. The energized relay 194 Ycloses the movablecontacts 196 and 197 to discharge the capacitor 190 and apply a positivepulse through themovable contact 144, now in the upper position, tocause the tube 138 to become conductive and the tube 139 to cutoff. Therelay 141 is deenergized so that the positive voltage is applied throughthe movable -contact 147 to energize the relays 157 and 159. With therelays 157 and 159 energized, the positive illuminating signal isapplied through the movable contact 161 and 153 to the eastbound greenand through the movable contacts 163 andY 155 to the Westbound green. Atthis point a completeV cycle of operation has been completed.

Where the primary street carries northbound and southbound traic, asillustrated herein, the variable resistors 173, 187, 198 and 201 aregiven different settings to permit the north-south green signals toremain illuminated for a greater portion of each cycle than theeast-West green signals. To illustrate, the timing circuit 132determines the interval during which a yellow signal is displayed forall four directions, so that the resistors 187 Y and 201 are set withlow resistance values to provide comparatively short intervals. Both ofthe resistors 173 and 198 of the timing circuit 134 are set tocomparatively large resistance values, which are capable of producingsubstantially longer charging intervals than in the other timing circuit132. However, the resistance value of the resistor.173 may be madesomewhat smaller than the resistance value for the resistor 198, sincethe resistor 173 controls the interval during which an eastbound andwestbound green signal remains.

In order to provide the proper interrelation between the operations ofthe left turn signal unit 86 and the four-way traffic control unit 122,interconnections are provided between the two units on the fourconductors 211, 212, 213 and 214. The purpose of these interconnectionsis best understood by considering the operation of the left tum signalunit 86 upon receipt of a turn left indication from the time averagingand comparing circuit 60.

The turn left indication is applied as a positive voltage to energizethe relay 94 and gradually charge the capacitor 106 through the variableresistor 104. The energized relay 94 disconnects the movable contact 96from the ground potential at its upper xed contact and connects itthrough the diode 102 to the conductor 211. The conductor 211 isdirectly connected to the southbound red signal of the display 127.Therefore, if the southbound red signal is receiving an illuminatingvoltage, the same voltage is applied through the conductor 211, diode102, the movable contact 96 and the small resistor 10S to quickly chargethe capacitor 106, which otherwise would be more gradually chargedthrough the resistor 104.

In addition, energizing of the relay 94 removes the ground potentialfrom the conductor 214, thus preventing any current ow through the relay171. Therefore, if the southbound display 127 previously displayed agreen signal, then a yellow signal now results.

When the capacitor 106 is charged sufiiciently, the resulting conductionof the tube 110 energizes the relay 112 to disconnect the groundpotential from the conductor 213. 1f previously energized, the relay 169is now deenergized so that the movable contact 175 applies anilluminating signal to the southbound red signal. Also the illuminatingvoltage to the northbound green signal is applied through the conductor212 and the movable contact 118 to illuminate the turn left arrow 92.Thus, the interconnecting conductors 211-214 permit operation of theleft turn signal unit 86 only when the proper signals have beendisplayed on the four-way signal unit 122.

For example, assuming that a turn left indication is produced by thedemand of left turning ve-hicles during an interval in which northboundand southbound trafiic is owing, the capacitor 106 begins to graduallycharge while the southbound display 127 changes from green to yellowWhen capacitor 106 has charged suiciently, the relay 112 is energized toapply an illuminating signal to the left turn arrow 92 and to insure thedisplay of a southbound red signal through deenergization of the relay169. If on the other hand, the turn left indication results whennorthbound and southbound traffic is stopped by a red signal, the relay112 is almost immediately energized along with the relay 94 to preventthe occurrence of a southbound green signal and to connect thenorthbound green signal to the left turn signal 92. Accordingly, as thefour-Way signal unit 122 advances through its normal cycle to display aneastbound and westbound red signal, the southbound signal remains redwhile an illuminating voltage is applied to the northbound green signaland through the conductor 212 to the left turn arrow 92. Thus, in bothcases, eastbound, westbound and southbound trafiic is stopped to permitnorthbound vehicles to turn left.

Although a preferred embodiment of the invention has been illustratedand described herein, by way of example, it 'will be appreciated thatthe system and its parts may be adapted, modified or changed withoutdeparting from the invention as set forth in the appended claims.

What is claimed is:

1. A traiiic control device for regulating vehicular flow in a primaryand secondary direction at an intersection, the vehicular flow in eachdirection -interfering with traffic flow in the other direction,comprising:

first and second detecting means for sensing the presence of vehiclesand for providing separate first and second output signal levelsindicative of the number of vehicles approaching the intersection insaid primary and secondary directions, respectively;

rst and second time averaging .circuits coupled to receive the rst andsecond output signal levels and for providing separate first and secondaveraged voltage levels proportional to a time average of the number ofvehicles approaching in either direction;

a preset voltage level source;

rst signal comparing means coupled to receive the preset voltage levelfrom said source and the Iaveraged voltage level from said first timeaveraging circuit;

a first trafiic control signal for forbidding traiiic iiow in thesecondary direction coupled to said first comparing means to be`actuated whenever the first averaged voltage level from said first timeaveraging circuit exceeds said preset level;

second signal comparing means coupled to receive the averaged Voltagelevels from the rst and second time averaging circuits and for providingan actuating signal whenever the output voltage level from said secondtime averaging circuit is greater than the output voltage level fromsaid iirst time averaging circuit;

gating means responsive to an enabling signal for passing the actuatingsignal from the second comparing means, said first comparing meansproviding an enabling signal to said gating means whenever the rstVaveraged voltage level is less than the preset voltage level; and

a second traffic control signal coupled to the output of said gatingmeans and responsive to the actuating signal passed by the gating meansto stop traffic in the said primary direction and permit trafiic flow insaid secondary direction.

2. An intersection traflic control system for regulating the ow ofvehicular traflic at an intersection in a primary and secondarydirection comprising:

first detector means for sensing the presence of vehicles approachingsaid intersection from said primary direction and providing a firstoutput signal representing a time average of the number of vehiclessensed;

second detector means for sensing the presence of vehicles approachingsaid intersection from said secondary direction and providing a secondoutput signal which is a time average of the number of vehicles sensed;

a voltage source for providing ya third output signal at a preset level;

first signal comparing means for comparing the levels of the firstoutput signal with the preset level of the third output signal from thevoltage source;

second signal comparing means for comparing the levels of the first andsecond output signals; and

a traffic signal control means responsive to the first and second signalcomparing means, said traffic signal control means operating to forbidthe vehicular flow in said secondary direction whenever the level of thefirst output signal is above the preset level of said third outputsignal, and to permit the vehicular flow in said secondary directionwhenever the level of the iirst output signal is below the preset leveland the level of the second output signal is `above the level of thefirst output signal.

3. A traic signal device for controlling the turning of veh-icles from=a first direction across the path of oncoming vehicles from theopposite direction comprising:

first means for deriving a iirst signal level indicative of the traicflow in the oncoming direction;

second means for deriving a second signal level indicative of the numberof vehicles waiting to turn;

a -traflic control signal means responsive to command signals andincluding fa first visual signal for forbidding turns, a second visualsignal for permitting waiting vehicles to turn, and a third signalindicating said turns will be permitted upon the occurrence of thesecond signal;

1 1 1 2 iirst comparison means for comparing the iirst signal 6. Thedevice of claim 5 wherein .said traflic signal level from said firstmeans with a predetermined control means further includes level -toprovide a first command signalV to actuate 'means responsive to theopening of said second switch said first visual signal whenever saidiirst signal level for forbidding the ow of turning vehicles across fromsaid first means exceeds a predetermined level 5 oncoming trafic fromthe opposite direction; and and to provide a second command signal toactuate means responsive to the closure of said second switch said thirdvisual signal whenever said first signal and the opening of said firstswitch for conditionally level does not exceed said predetermined level;permitting the ilow of turning vehicles across oncomsecond comparisonmeans for comparing the first yand ing trafiic when said iirst switch isalso closed.

second signal levels to provide a third command sig- 7. The device ofclaim 6 wherein said trafiic control nal for actuating said secondvisual signal; and signal means includes gating means coupled betweensaid second comparison a cyclically operated stop-go trafiic lightarrangement,

means and said second signal for -passing said third and command signalto actuate said second signal only means interconnecting said cyclicallyoperated traffic when the gating means is enabled by the second controlarrangement to operate in synchronism with command signal from saidfirst comparison means. the signal for permitting the l'low of turningvehicles 4. A trafiic control device for -controlling the turning acrossoncoming traiiic. of vehicles across oncoming trafiic -from the opposite8. The traic Control device of claim 7 further indirection comprising: ncluding first detection means for measuring the now of oncoma cyclicallyoperated four-way traffic control signal for ing traffic in saidopposite direction and providing starting and stopping the ow ofvehicles on the two a first output signal indicative thereof; streets;and rst comparing means for comparing said first output meansinterconnecting said comparing means with said signal from said firstdetection means with a precyclically operated four-way traic controlsignal determined signal level; for stopping said trafc in the oncominglanes and second detection means for providing a second outputpermitting the ow of turning vehicles.

signal indicative of a time `average of the number of 9, A trafficcontrol device for controlling the flow of vehicles waiting to turn;vehicles at an intersection of a main street and a cross secondcomparing means for comparing the first and street comprising:

second output signals from said first and second a four-way trafficcontrol signal cyclically operated to detection means; and permit theflow of traf'lic on the main street through a turn control signal forStopping the ow of oncomthe intersection during a first portion of acycle and ing trafiic to allow the waiting cars to turn, said turn toPermit trame to lloW through the interSeCtion control signal beingoperated by circuit means, said from the cross Street during a secondportion of the circuit means being responsive to command signals Cycle;from said first and second comparison means indicati lirSt detectlngmeans reSPonSiVe to the number of oni ing that the first output Signal.is less than Said precoming vehicles present in a given area adjacentsaid determined level and Said Second output signal is intersection forproducing a firist signal level indicagreater than Said rst outputsignal, tive of the time average of the number of vehicles 5. A traiccontrol device for controlling vehicles 40 detected; t turning acrossoncoming trafiic approaching an intersec- Second detecting meanSreSPonSiVe to the number of tion from an opposite direction comprising:vehicles that approach the intersection from the a plurality of vehicledetectors vfor providing a first opposite direction Which are Withinanother area signal level indicative of the number of oncoming adlacentSeid interSection intending to turn aCroSS vehicles in a given areaadjacent the intersection; the oncoming tronic, .Salvo Second meansProviding' a second plurality of vehicle detectors for providing a aSecond Signal level mdlcatlVe of the tlme aVerage ofthe number ofturning vehicles present;

means for comparing said first and second signal levels for prohibitingthe vehicles within said another area from turning unless said secondsignal level exceeds said first signal level; and Y meansinterconnecting said comparing means with said four-way traffic controlsignal to cause said fourway trafiic control signal to display a stopsignal to the oncoming traiiic and to the cross street traffic to secondsignal level indicative of the number of turning vehicles in a givenarea adjacent the intersection;

first means for integrating said first output signal to provide a time:average of the number of oncoming vehicles detected;

second integra-ting means for providing a time average of the number ofturning vehicles detected;

means providing a predetermined signal level for comparison with saidfirst time average signal;

a unidirectional diode coupled between said predetermined signal levelmeans and said rst and second integrating means in a direction toconduct current only when the level of said first time average ex ceedssaid predetermined level; Y 6

a second unidirectional diode coupled between said first and said secondtime average signal means in a direction to conduct only when the levelof s-aid second time average signal exceeds the level of said first timeaverage signal;

first relay means responsive to the conduction of current through saidfirst unidirectional diode -for `closing a first switch;

second relay means responsive to the conduction of mined portion of eachsaid cycle.

10. The device of claim 9 further including another traine controlsignal for forbidding the vehicles in said another area from turningwhenever said first signal exceeds a predetermined level.

11. A trafiic control device for regulating the ilow of traffic in twodirections through an intersection comprising:

a first vehicle detection means for providing a first output signalproportional to the number of vehicles approaching the intersectiontraveling from a first of the two different directions;

a second vehicle detection means for providing a seccurrent through saidsecond unidirectional diode to 0nd Output Signal Proportional t0 thenumber of close second Switch; and vehicles approaching the intersectionfrom the second a traiiic signal responsive to the closure of both saidofthe tWo different directionS;

lirst `and second switches to permit the turning of the e irStintegrating circuit including a lirSt integrating vehicles acrossoncoming traffic from the opposite capacitor and a first resistor forlimiting the flow of direction. charging current to the capacitor;

permit the turning of vehicles during a predetera second time averagingcircuit including a second integrating capacitor and a second resistorfor limiting the fioW of charging current to the capacitor;

a first diode, means connecting the first diode to conduct current to afirst terminal when the voltage level on said rirst integratingcapacitor exceeds the voltage level on said second integratingcapacitor;

a second diode, means connecting the second diode to conduct current toa second terminal when the voltage level on said second integratingcapacitor exceeds a predetermined level;

first circuit means including said first and second terminals;

a first trafiic control signal means controlled by said first circuitmeans for forbidding the fiow of traffic in the first direction when thesecond diode conducts current to the second terminal;

a second traic control signal means controlled by said first circuitmeans for indicating that trafiic Will be permitted to flow in the firstdirection when no current is conducted by the second diode to the secondterminal; and

a third trafiic control signal means controlled by said first circuitmeans for stopping trafiic in the second direction and permitting thefiow of trafiic in the first direction through the intersection when nocurrent is conducted by the second diode to the second terminal and thelirst diode conducts current to the first terminal.

12. The traic control system of claim 11 further comprising:

cyclic trafiic control means associated with said first circuit meansfor intermittently permitting traic in the second direction, and whereinsaid first, second and third trafiic control signals control vehiclesapproaching the intersection from the first direction and turning acrossoncoming traiic from the second direction; and

second circuit means associated with said third trafiic control signaland coupled to said first circuit means for synchronizing the actuationof the first, second and third trafiic control signals with theoperation of the cyclic traliic control means.

13. A trafiic control device for regulating the flow of 'trafiic throughan intersection of a primary street with a secondary street comprising:

trafiic control signal means for alternatively displaying go and stopsignals to traic approaching the intersection on the primary andsecondary streets, the .tratc control signal means having means forautomatically controlling the display of a stop signal to approachingtrafiic on the secondary street during a first portion of a cycleinterval and displaying a stop signal to trafic approaching on theprimary street during a second portion of -a cycle interval;

a first vehicle presence detector means responsive to the number ofvehicles approaching the intersection from a first direction on theprimary street for providing a time average of the number of vehiclesdesiring to turn left across oncoming traffic;

a second vehicle presence detector means responsive to the number ofvehicles approaching the intersection from the oncoming direction on theprimary street for providing a time average of the traffic ow in theoncoming direction;

turn signal means including circuit means coupled to the first andsecond vehicle presence detector means, said turn signal means being`operative to display a signal forbidding turns of traffic from saidfirst direction across the oncoming direction Whenever the time averageof the oncoming traic is above a predetermined level, said turn signalmeans being further operative to display a signal conditionallypermitting said turn when the time average of the oncoming traliic isbelow a predetermined level, and said turn signal means being stillfurther operative to display a signal permitting said turns whenever thetime average of the number of vehicles Waiting to turn exceeds the timeaverage of the oncoming traffic and the time average of the oncomingtrafiic is below the predetermined level; and

means interconnecting the turn signal means With the intersection traiccontrol signal means for coordinating the operation of both signal meansso that the signal permitting left turns is displayed only during thesecond portion of the cycle interval and assuring that a stop signal isdisplayed to the approaching trafiic on the secondary street and theoncoming tratiic on the primary street.

14. A traffic control device for regulating vehicular flow in a primaryand secondary direction at an intersecv tion, the vehicular flow in eachdirection interfering with trafiic liow in the other direction,comprising:

first detection means for measuring the flow of traiiic approaching theintersection in said primary direction and providing a first outputsignal indicative thereof;

first comparing means for comparing said output signal from said firstdetection means with a predetermined signal level;

second detection means for measuring the flow of traffic approaching theintersection in said secondary direction and providing a second outputsignal indicative thereof;

second comparing means for comparing the first and second output signalfrom said first and second detection means; and

a traffic lcontrol signal to stop traffic in the said primary directionand permit traffic How in said secondary direction, said traflie controlsignal being operated by circuit means, and said circuit means beingresponsive to command signals from said first and second comparisonmeans indicating that the first output signal is less than saidpredetermined level and said second output signal is greater than saidrst output signal.

References Cited UNITED STATES PATENTS 2,542,978 2/1951 Barker 340-352,750,576 6/1956 Beaubien 340-35 2,883,644 4/1959 Barker 340-363,208,038 9/ 1965 Jeffers 340-35 FOREIGN PATENTS 992,198 10/1951 France.

NE1L C. READ, Primary Examiner.

THOMAS B. HABECKER, Examiner.

1. A TRAFFIC CONTROL DEVICE FOR REGULATING VEHICULAR FLOW IN A PRIMARYAND SECONDARY DIRECTION AT AN INTERSECTION, THE VEHICULAR FLOW IN EACHDIRECTION INTERFERING WITH TRAFFIC FLOW IN THE OTHER DIRECTION,COMPRISING: FIRST AND SECOND DETECTING MEANS FOR SENSING THE PRESENCE OFVEHICLES AND FOR PROVIDING SEPARATE FIRST AND SECOND OUTPUT SIGNALLEVELS INDICATIVE OF THE NUMBER OF VEHICLES APPROACHING THE INTERSECTIONIN SAID PRIMARY AND SECONDARY DIRECTIONS, RESPECTIVELY; FIRST AND SECONDTIME AVERAGING CIRCUITS COUPLED TO RECEIVE THE FIRST AND SECOND OUTPUTSIGNALS LEVELS AND FOR PROVIDING SEPARATE FIRST AND SECOND AVERAGEDVOLTAGE LEVELS PROPORTIONAL TO A TIME AVERAGE OF THE NUMBER OF VEHICLEAPPROACHING IN EITHER DIRECTION; A PRESET VOLTAGE LEVEL SOURCE; FIRSTSIGNAL COMPARING MEANS COUPLED TO RECEIVE THE PRESET VOLTAGE LEVEL FROMSAID SOURCE AND THE AVERAGED VOLTAGE LEVEL FROM SAID FIRST TIMEAVERAGING CIRCUIT; A FIRST TRAFFIC CONTROL SIGNAL FOR FORBIDDING TRAFFICFLOW IN THE SECONDARY DIRECTION COUPLED TO SAID FIRST COMPARING MEANS TOBE ACTUATED WHENEVER THE FIRST AVERAGED VOLTAGE LEVEL FROM SAID FIRSTTIME AVERAGING CIRCUIT EXCEEDS SAID PRESET LEVEL; SECOND SIGNALCOMPARING MEANS COUPLED TO RECEIVE THE AVERAGE VOLTAGE LEVELS FROM THEFIRST AND SECOND TIME AVERAGING CIRCUITS AND FOR PROVIDING AN ACTUATINGSIGNAL WHENEVER THE OUTPUT VOLTAGE LEVEL FROM SAID SECOND TIME AVERAGINGCIRCUIT IS GREATER THAN THE OUTPUT VOLTAGE LEVEL FROM SAID FIRST TIMEAVERAGING CIRCUIT; GATING MEANS RESPONSIVE TO AN ENABLING SIGNAL FORPASSING THE ACTUATING SIGNAL FROM THE SECOND COMPARING MEANS, SAID FIRSTCOMPARING MEANS PROVIDING AN ENABLING SIGNAL TO SAID GATING MEANSWHENEVER THE FIRST AVERAGED VOLTAGE LEVEL IS LESS THAN THE PRESETVOLTAGE LEVEL; AND A SECOND TRAFFIC CONTROL SIGNAL COUPLED TO THE OUTPUTOF SAID GATING MEANS AND RESPONSIVE TO THE ACTUATING SIGNAL PASSED BYTHE GATING MEANS TO STOP TRAFFIC IN THE SAID PRIMARY DIRECTION ANDPERMIT TRAFFIC FLOW IN SAID SECONDARY DIRECTION.